Method of making cast squirrel cage rotors



Jan. 30, 1945. s. J. GORAN 2,368,295

METHOD OF MAKING CAST SQUIRREL CAGE ROTORS Filed Sept. 14, 1942 3 Sheets-Sheet 1 Jan. 30, 1945. s. J. GQRAN 2,368,295

METHOD OF MAKING CAST SQUIRREL CAGE ROTORS Filed Sent. 14, 1942 s Sheets-Sheet 2 Jan. 30, 1945. 5. J. GORAN METHOD OF MAKING CAST SQQIRREL CAGE ROTORS Filed Sept. 14, 1942 3 Sheets-Sheet 3 Patented Jane 30, 1945 UNITED STATES METHOD or MAKING CAST seminar-:1.- CAGE noroas Steven J. Goran, Milwaukee, Wis, assignor to The Louis Allis Company, Milwaukee, '15., a corporation of Wisconsin Application September 14, 1942, Serial No. 458,258

6 Claims.

This invention relates to electric motors and refers particularly to the construction of a squirrel cage rotor having cast conductor bars.

To those skilled in the art the necessity for providing ventilation for the rotor of a dynamo electric machine to carry oil the heat from the interior thereof is well understood. Many diiierent schemes have been employed for this purpose, and as an illustration of past practice,

reference may be had to Patent No. 2,176,871,

. tion to provide a squirrel cage rotor of the die cast type and a method of making the same wherein radial ventilating openings are formed between adjacent groups of laminations through the provision of temporary spacers which are 'removed after the casting operation.

It is also an object of this invention to provide a, method of making a rotor of the character described, whereby during the casting operation enlargements are automatically formed on the conductor bars between the groups of laminations to hold the same properly spaced.

Another object of this invention is to provide a method of making a rotor construction of the character described, wherein the temporary spacers used to form the radial ventilating openings are punched on the same dies used to punch the laminations so that the incorporation of the spacers involves no radical changes in method or procedure now employed in the making of such squirrel cage rotors.

With the above and other objects in view which will appear as the description proceeds, this invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described, and more particularly defined by the appended claims, it being understood'that such changes in the precise embodiment of the hereindisclosed invention may be made as come within the scope of the claims.

The accompanying drawings illustrate one complete example of the physical embodiment of the invention constructed in accordance with,

the best mode so far devised for the practical application of the principles thereof, and in which:

Figure l is a view partially in side elevation I and partially in longitudinal section through a die cast squirrel cage rotor embodying this invention;

Figure 2 is a perspective view of one of the laminations of the rotor and one of the temporary spacers used in the making of the rotor; Figure 3 is a view'inside elevation illustrating the manner in which the laminations and the temporary spacers are assembled on a mandrel preparatory to the die casting operation; Figure 4 is a view similar to Figure 3 but showing the rotor laminations fully assembled; Figure 5 is a logitudinal sectional view through a rotor in position in a casting mold preparatory to having the conductor bars cast into the slots; Figure 6 diagrammatically illustrates a step in the operation of manufacture following the casting;

Figure 7 is a diagrammatic illustration showing one manner of removing the temporary spacers; and

Figure 8 is a perspective view illustrating a section of the cast conductor bars to show the manner in which enlargements are formed thereon to space the groups of laminations.

Referring now particularly to the accompanying drawings, in which like numerals indicate like parts, the numeral 5 designates generally the core of a squirrel cage rotor which, as is customary, consists'of a'stack of laminations 6 all punched by the same die to have conductor bar slots 1 in their outer peripheral portions and longitudinal vent forming openings 8 surrounding a central shaft receiving hole 9.

The laminations 6 are confined between end plates ID or a. diameter to extend approximately to the roots or inner ends of the slots 1. These end plates l0 have circumferentially arranged openings II to align with the openings 8 of the laminations so that a plurality of longitudinal air passages l2 extending entirely through the core surround the shaft l3 upon which the core is mounted.

The entire structure is held together by conductor bars M which are die cast of aluminum or other suitable metal into the slots 1, the laminations being so arranged that the slots are slightlyskewed around to give the conductor bars the desired angle across the surface of the rotor.

The ends ofthe conductor bars are integral with rings l5 which overhang the end plates l0 and thereby tie the entire structure together. v

To this extent the present rotor follows conventlonal'practice, but it is to be observed that in addition to the longitudinal passages I2 there are I also radial vents or passageways 16 leading outwardly from the longitudinal passages 12 to the peripheral surface of the rotor, and that these radial passages or vents lie between adjacent groups of laminations which are held spaced aput at the inside by spacer collars ll of steel or other suitable metal and at the outside by integral enlargements or lugs H on the conductor bars In this manner an exceedingly simple and ine nsive construction is obtained for the provision of the desired radial air vents involves no costly or complicated spacing discs or their equivalent. The production of these desired radial vents is also accomplished in an exceedingly simple and inexpensive manner requiring no deviation from accepted practice in the manufacture of the die cast squirrel cage rotors.

To accomplish this objective, spacers I 8 are punched on the same dies used to punch the laminations, and these spacers are interposed between the groups of laminations during the assembly of the laminations, and afterthe casting operation they are removed.

To enable removal of the spacers after the casting operation they are punched of sheet material which may be readily decomposed. Cardboard is well suited for this purpose as it can be charred or carbonized by baking at temperatures which do not affect the cast conductor bars and when so decomposed can be easily removed by a blast of compressed air or the like as illustrated in Figure '7.

Another very important advantage of the use of cardboard or some such similar combustible material resides in the fact that during the cast-.

ing operation (illustrated in Figure the hot molten metal coming in contact with the spacer burns away the portions thereof adjacent to the slots to form the enlargements 0r lugs M on each conductor bar which, as hereinbefore noted space the adjacent groups of laminations around the periphery of the rotor.

Inasmuch as the spacers are preferably formed of cardboard or some such material which obviously does not have the same compressive strength as the metal laminations, the spacing collars I l are used to prevent collapse of the V spacersduring the application of compression on the stack, and to accommodate the collars I! the spacers have their central portions cut away as shown in Figure 2. The inwardly directed projections [9 on the spacers are of such siz as to just contact the outer diameter of the collars H.

In the actual making-of the rotor the stack of laminations with the req e number of spacers l8 interposed at the proper places is assembled as illustrated in Figures 3 and-4 on a mandrel 20. A slightly spiral keyway 2'! in the mandrel receives inwardly directed lugs or teats on the laminations to so dispose the laminations that their slots 7 will be skewed as required.

With the complete stack of laminations and spacers properly assembled on the mandrel the entirety is placed in a casting mold as shown in Figure 5. This mold is of conventional construction and includes a cylinder or well 22 in which a plunger 23is reciprocally received. The plunger 23 provides the base for the assembled core laminations and is formed to receive the lower end of the mandrel 20.

It is to be observed that the base 23 closes the longitudinal passageways l2 at the bottom. Hence molten metal cannot enter these passagewaysfi With the assembled laminations positioned on the base 23 a sheath 24 of sheet metal is applied around the cylindrical surface of the assembly to close the conductor bar slots 1; and then a cap 25positioned on the assembly which, like the base 23, is formed to accommodate the mandrel.

'28 of a size and shape to form the cast rings l5 and that the base has ports 29 leading to its channel 28 through which the molten metal enters the same and consequently rises up into the conductor bar slots during the casting operation.

It is, of course, understood that the assembly of the core structurein the mold as described takes place before the well or cylinder 22 has the molten metal poured into it, and that after the assembly is completed the cap which is attached to the plunger 30 of a hydraulic press is raised to lift the entire assembly out of the well and permit ladling of the molten metal into the well. Thereafter the plunger 30 is caused to descend which forces the molten metal up into the slots and the channel 28 in the cap.

Air vents 3| in the cap preclude the entrapment of air and permit the metal to rise up into the slots.

As the molten metal rises up into the conductor bar slots it comes in contact with the illustrated in Figure 6, or otherwise subjected to an elevated temperature to char or carbonize the spacers.

If cardboard is used as the material for the spacers a temperature of about 700 F. is sufficient to eifect the desired decomposition. Ob-

viously, if some other material is employed for the spacers the temperature required to effect the necessary decomposition may have to be higher, but in no event should the heat treatment reach the temperature at which the cast conductor bars and end rings would be affected.

It will be readily apparent that the desideratum of this invention can be achieved with a wide variety of materials for use as the temporary spacers and that the material of which the spacers are made does not have to be combustible. For instance, a material which is readily soluble in a suitable solvent but which is not afiected by elevated temperatures could be used. In this case, the apertures in the spacer which align with the conductorbar slots would be somewhat larger than the slots 7 of the' laminations to enable the molten metal to form the enlargements or lugs I4.

In all instances, however, the material used for the temporary spacers must be capable of decomposition. Hence, wherever this term is employed in the specification and claims it is to be understood that it covers not only a combustible material but any substance which. through any suitable treatment, can be easily decomposed to enable removal of the spacers after the casting operation.

In the embodiment of the invention illustrated the laminations are provided with punched openings to form the longitudinal ventilating passages and the laminations are mounted directly on the rotor shaft. Obviously, the same result can be obtained by following the conventional practice of applying the rotor core, that is the stack of laminations, on a spider which in turn is mounted on the rotor shaft. This common expedient is illustrated in the aforesaid patent to Harrell et al.

From the foregoing description, taken in connection with the accompanying drawings, it will be readily apparent to those skilled in the art that this invention provides an exceedingly simple and inexpensive manner of making squirrel cage rotors of the type having die cast conductor bars.

What I claim as my invention is:

1. The hereindescribed method of making a squirrel cage rotor having cast conductor bars embedded in slots in a laminated core which comprises: assembling the laminations of the core with their slots properly aligned and with the laminations divided into at least two groups held spaced apart by a .spacer of combustible material which extends to the periphery of the laminations but does not close the conductor bar slots; casting the conductor bars into said slots so that the hot molten metal burns away part of the spacer and overruns the edges of the slots in the adjacent laminations-to form lugs integral with the conductor bars and between said laminations to hold the groups of laminations spaced apart; subjecting the rotor after the casting operation to a temperature high enough to carbonize the spacer but not high enough to affect the cast conductor bars; and subsequently removing the carbonized spacer to form radial ventilating passages between the conductor bars and said groups of laminations.

2. The hereindescribed method of making a souirrel cage rotor having cast conductor bars embeddedin aligned slots in a stack of punched laminations which comprises: punching a spacer of readily decomposable material to give the spacer the same size and configuration as the outer portion of the laminations; interposing the spacer between two adjacent inner laminations with its slots in line with those of the laminations so that the presence of the spacer does not disturb the continuity of the conductor bar slots formed in the core upon completion of the assembly of the laminations; casting the rotor bars into said slots with the metal of the conductor bars flowing over the edges or the conductor bar slots in the laminations between which the spacer is confined to form enlargements or lugs integral with the conductor bars for holding the groups of laminations spaced apart at the conductor bars; and subsequently destroying the spacer so as to leave ventilating air passages extending radially between said conductor bars and between said adjacent laminations.

3. The hereindescribed method of making a squirrel cage rotor having cast conductor bars embedded in the aligned slots" of a stack of punched laminations which comprises: punching a spacer out or combustible material and to the same size and configuration as the outer portion of the laminations so as to provide the same with similarly haped and located conductor bar slots; assembling the laminations in a stack with the spacer interposed between two adjacent laminations and with the conductor bar slots of the laminations and spacer aligned so as to form continuous slots for the reception of themolten metal which is to form the con ductor bars; casting the conductor bars in said slots so as to bum away part of the spacer I adjacent to the slots therein by the molten metal flowing into the slots to thereby form enlargements on the conductor bars between said adjacent inner laminations; and subsequently destroying and removing the combustible spacer so as to form radial ventilating passages between the'conductor bars and between said two adjacent inner laminations.

4. In a method of making a squirrel cage rotor having cast conductor bars embedded in aligned slots in a stack of punched laminations: the steps of punching the spacer out of readily combustible material to the same size and configuration of at least the outer portion of the punched laminations so that said spacer has similarly formed and located conductor bar slots: assembling the laminations with the spacer between two inner laminations and with the conductor bar slots properly aligned; casting conductor bars into said slots and simultaneously burning away the portions of the spacer adjacent to the conductor bar slots therein by the molten metal flowing into the slots so that spacing enlargements are formed integrally with the conductor bars and between said two adjacent inner laminations; heating the rotor to carbonize the remainder of the spacer; and removing the carbonized spacer material so as to leave radial ventilating passages extending between the conductor bars and between said adjacent laminations.

5. In the manufacture of laminated squirrel cage rotors having cast conductor bars embedded in aligned slots in the laminations and having a solid spacing collar interposed between tWo' adjacent inner laminations at the hub of the rotor to divide the stack of laminations'lnto two groups: the steps of punching the laminations and a temporary spacer of readily decomsquirrel cage rotor having posable material on the same die to provide the laminations and the temporary spacer with conductor'bar slots in their outer peripheral portions; assembling the laminations with the solid spacing collar and the temporary spacer surcol lar between the two groups of laminations; clamping the entire stack of laminations with the collar and the temporary spacer in position; casting the conductor bars into the aligned conductor bar slots of the laminations and the temporary spacer with the metal of the conductor bars flowing over the edges of the conductor bar slots of the laminations between which the spacer is confined to form enlargements with the conductor bars for holding the groups'oflaminations spaced apart at the conductor bars; and removing the spacer from between said two groups of laminations so as to form radial ventilating passages between the conductor bars. I

6. In the hereindescribed method or making a cast conductors bars in a stack of lamirounding the embedded in aligned slots nations, the steps of: segregating the stack of laminations into at least two groups; holding said two groups of laminations spaced apart but .with their conductor bar slots properly aligned;

casting conductor bars into the slots and across the space between the two groups of laminations ,to connect the groups by bridging portions of the conductor bars; and confining the molten metal which is to form the bridging portions of the conductor bars to the region of the con ductor bar slots in the adjacent laminations while allowing the molten metal to flow over the edges of the conductor cent laminations so as to form shoulders integral with the conductor bars and engaging the adjacent laminations of the two groups to hold the groups spaced apart.

STEVEN J. GORAN.

bar slots in said adja- 

